The present invention relates generally to a ball drop tool, and more particularly to a ball drop tool to be connected in a tool string lowered into a wellbore with coiled tubing.
In the drilling and completion of oil and gas wells, a wellbore is drilled into the subterranean producing formation or zone of interest. A string of pipe, e.g., casing, is typically then cemented into the wellbore. Oftentimes, a second string of pipe, commonly referred to as a liner, is attached at the lower end of the casing and extends further into the wellbore. Casing, when referred to herein, includes liners. A string of additional pipe, known as production tubing, is often lowered into the casing and/or the liner for conducting produced fluids out of the wellbore.
It is often necessary to lower downhole tools, such as packers or other tools into the casing, liner or production tubing to perform a desired operation. Many known downhole tools, such as but not limited to hydraulic disconnects, circulating subs, and inflatable packers require a ball to be displaced down a tool string to engage a ball seat disposed in the tool. Typically, pressure is applied after the ball engages the seat to actuate a mechanism in the tool. For example, with an inflatable packer, the ball may engage a seat to direct fluid into the inflatable elements of the packer, so that the packer will engage the casing, liner, or production tubing. The foregoing are merely examples and there are a number of known tools that utilize and require a ball to engage a ball seat so that pressure can be applied in the tool above the seat to actuate a mechanism in the tool string.
Coiled tubing is a popular conveyance method for downhole tools, and the use of dropped balls to engage a seat in a tool lowered into the wellbore with coiled tubing is becoming more and more common. When coiled tubing is utilized to lower a tool into a wellbore, and it is necessary to drop a ball to engage a seat in the tool, the ball may be manually inserted into the surface plumbing for the coiled tubing, so that the ball enters the coiled tubing at, or near the end of the tubing connected to the surface plumbing. The ball therefore enters the coiled tubing so that it must be pumped through the coiled tubing wraps on the reel, until it passes over a gooseneck which is utilized in connection with the coiled tubing. Pumping then continues for a period of time to ensure that the ball has made its way through the coiled tubing to the seat in the downhole tool. Although such a method works in many circumstances, there are several drawbacks to this method.
The method described above for displacing a ball through coiled tubing is time-consuming and costly. It requires the usage of a large volume of fluid since at least one displacement volume of the coiled tubing is needed to get the ball around the wraps and to the downhole tool. Occasionally, balls are caught in the coiled tubing and never make it to the tool.
In addition, there are times when downhole devices above the ball seat have restrictions which would prevent a ball from passing therethrough to the ball seat in the tool. For example, filter screens are often run downhole to keep debris from plugging off small passages in the tools below. Actuating balls cannot pass through the screens. Likewise, it is possible that a tool having a small diameter would be positioned above the ball seat and thus would prevent the ball from passing therethrough. The invention disclosed in U.S. Pat. No. 6,220,360 (the '360 patent), owned by the assignee of the current invention, which is incorporated herein by reference in its entirety, addresses these needs by providing a flow-activated ball dropper that carries an actuating ball into the well and launches the ball when a predetermined flow rate is achieved. While the invention described in the '360 patent works well, there is a continuing need for new methods and apparatus that can be used when devices in a tool string have restrictive diameters or flow passages that would prevent an actuating ball or other actuating device of a desired size from passing therethrough. The present invention addresses the above needs by providing a downhole ball drop tool that can be positioned in the tool string below any tools with restrictive diameters or flow passages, and above the actuating seat in the tool such that the ball does not have to pass through restrictive flow passages. The ball drop tool of the current invention will release the actuating ball at a desired time, and provides certainty that the actuating ball has been released to engage the actuating seat.